a. Field of Invention
The invention pertains to the field of on-board networks for motor vehicles and more particularly to an on-board network equipped with a multiplex control for switching, controlling and monitoring electrical end devices such as lights, windows, and so on.
b. Description of the Prior Art
Through technical development, the functional performance of motor vehicles, the ease of operation and the comfort of the occupants have been improved substantially in recent years. These improvements resulted in an extensive enlargement of the electrical equipment for motor vehicles. For connecting individual devices, wiring harnesses are used which sometimes contain line lengths of more than 500 meters of wires and over 1,000 electrical plug connections. These harnesses are of very complex design and are prone to manufacturing errors since the fabrication of a harness is done predominantly manually. Furthermore, the harnesses are sometimes difficult to install and have poor accessibility for repair purposes. It has therefore been proposed already to replace the wire-harness of a motor vehicle by an on-board network, in which particularly the different electrical end devices such as operating elements, sensors and similar devices (e.g., indicators, lamps, heaters, motors, actuators) being arranged in the periphery of the body and are interconnected through a multiplex-system which is superimposed on a power supply system. These known on-board networks consist of respective signal lines and electronic electrical subassemblies which are disposed at numerous points in the car. The subassemblies receive or deliver control and monitoring signals and also switch on or off electrical devices directly. The subassemblies are connected to each other via signal lines and signal converters, transmitters, receivers and control devices. The arrangement and connection of the subassemblies to each other is based either on a bus line, a ring or a star configuration. In on-board networks which consist of a bus line, several bus interfaces are connected to the bus line and peripheral end devices are associated with the bus interfaces, the bus interfaces are equipped for communication with each other with transmitters and receivers for the exchange of data signals. These on-board networks contain as a rule a multiplexer control and operate frequently by means of an asynchronous signal transmission and with random bus access for switching, controlling and monitoring the electrical end devices. Every bus interface contains an arbitration device for resolving conflicts in the case of simultaneous access requests of several bus interfaces to the bus line.
The state of the art is represented, for instance, by the following patents and articles: DE-A-24 33 025 DE-A-34 17 956 DE-A-35 45 293 DE-A-29 09 213 DE-A-34 29 941 EP-A-0 008 238 DE-A-31 49 142 DE-A-35 22 907 EP-A-0 014 556 DE-A-33 35 932 DE-A-35 35 860 EP-A-0 023 105 "Proposal for an Automotive Multiplex Firing System," No. C 205/85 in IMechE 1985, pages 227 to 230; "Systems Consideration for Incorporating Vehicle Data Networks (Multiplex) into Automobiles;" No. C 218/85 in IMechE 1985, pages 209 to 216; SAE Technical Paper Series No. 860389 "Chrysler Collision Detection (C.sup.2 D), a Revolutionary Vehicle Network."
In these known on-board networks, a complete system failure due to defects in a transmission line (in the case of a bus or a ring configuration) or due to the failure of the central station (in the case of a star configuration) can easily occur.